1. Field of the Invention
The invention relates to a plug-in hybrid vehicle that is able to charge a drive electrical storage device (hereinafter, referred to as “driving battery” or simply referred to as “battery” where appropriate) from an external power supply. Particularly, the invention relates to improvement in a method of calculating an electric power consumption rate. Note that “one trip” in the specification means a period from charging (plug-in charging) of the driving battery from the external power supply is completed and then the vehicle starts travelling to when the next plug-in charging is started.
2. Description of Related Art
In recent years, in terms of environmental protection, it is desired to reduce the amount of emission of exhaust gas from an internal combustion engine (hereinafter, referred to as “engine” where appropriate) mounted on a vehicle and to improve a fuel consumption rate (fuel economy). As a vehicle that satisfies these requirements, a hybrid vehicle equipped with a hybrid system has been practically used. The hybrid vehicle includes an engine, such as a gasoline engine and a diesel engine, and a driving motor (for example, formed of a motor generator or a motor) that is driven by electric power generated by the power of the engine or electric power stored in the driving battery. The hybrid vehicle travels by utilizing one or both of these engine and driving motor as a driving force source.
In recent years, a hybrid vehicle that is able to charge a driving battery, which supplies electric power to a driving motor, with electric power from a power supply outside the vehicle (external power supply), such as a domestic power supply (so-called plug-in hybrid vehicle) has been developed.
The plug-in hybrid vehicle is designed on the assumption that the vehicle travels preferentially on electric power from the driving battery in order to significantly improve a fuel consumption rate. For example, as is described in Japanese Patent Application Publication No. 2011-51395 (JP 2011-51395 A) and Japanese Patent Application Publication No. 2011-225097 (JP 2011-225097 A), a drive mode of a plug-in hybrid vehicle is set to a mode (generally, called “charge depleting (CD) mode” or “electric vehicle (EV) mode”) in which the vehicle travels preferentially on only the power of a driving motor until the state of charge of the driving battery decreases to a predetermined value, and is changed to a mode (generally, called “charge sustain (CS) mode” or “hybrid vehicle (HV) mode”) in which the vehicle travels preferentially on both the power of an engine and the power of the driving motor when the state of charge of the driving battery is lower than the predetermined value.
In addition, in the plug-in hybrid vehicle, when the vehicle travels on only the power of the driving motor in the CD mode, a distance-to-empty is calculated for the current state of charge (remaining state of charge) of the driving battery, and information about the current state of charge is indicated on a meter panel (instrument panel). More specifically, an electric power consumption rate is calculated (an electric power consumption rate is learned) from a previous driving condition (relationship between an electric power consumption and a travel distance). The electric power consumption rate is a travel distance per unit amount of electric power. A distance-to-empty is calculated by multiplying the electric power consumption rate by the state of charge (the amount of electric power that is usable until the state of charge reaches the predetermined value at which the drive mode is changed to the CS mode) of the driving battery.
In addition, Japanese Patent Application Publication No. 2009-290940 (JP 2009-290940 A) describes a method of calculating an electric power consumption rate, in which an electric power consumption rate is calculated on the basis of a power of a driving force transmission system at the time when a vehicle travels a specified road section.
In the case where an electric power consumption rate is calculated as described above, when an engine is driven, it is required to calculate the work of the engine and the amount of charge in the case where part of the power of the engine is utilized for power generation in a motor generator and then a battery is charged, so calculation of an electric power consumption rate may be complicated or may not have sufficient accuracy. Therefore, calculation of an electric power consumption rate (including the case where only information for calculating an electric power consumption rate (an electric power consumption and a travel distance) is acquired) is desirably performed on the basis of an electric power consumption in the case where the vehicle is travelling while the engine is stopped and a travel distance obtained from the consumed electric power.
However, the inventors of the present application found that, when an electric power consumption rate is calculated from only information (an electric power consumption and a travel distance) at the time when the engine is stopped in this way, there may be an inconvenience that will be described below.
Hereinafter, the inconvenience will be specifically described with reference to FIG. 11. FIG. 11 shows a gradient of a road surface and a variation in electric power consumption rate (value in the case where it is assumed that an electric power consumption rate is calculated at each timing; an electric power consumption rate gets better toward an upper side and gets worse toward a lower side) during a vehicle travel in the case where a plug-in hybrid vehicle HV travels on an uphill and then travels on a downhill. The electric power consumption rate is a value obtained by dividing a travel distance from a start of travel (start of trip) by an electric power consumption. The solid line in the drawing indicates a proper electric power consumption rate that should be originally obtained as a variation in electric power consumption rate.
For example, when the plug-in hybrid vehicle HV utilizes both the power of the motor and the power of the engine at the time of travelling on the uphill, the engine is driven in that period (t1 in the drawing), so information for calculating an electric power consumption rate (information about an electric power consumption and a travel distance) is not acquired. That is, the electric power consumption rate in the period t1 is constant (remains unchanged) as indicated by the alternate long and short dash line in the drawing. However, in this period t1, actually, the vehicle travels on the uphill and, therefore, the electric power consumption per unit travel distance is relatively large. If an electric power consumption rate is calculated by acquiring information about an electric power consumption and a travel distance, the electric power consumption rate becomes relatively bad (intrinsically, in the period t1, a variation in electric power consumption rate becomes the one indicated by the solid line). On the other hand, when the vehicle travels on the uphill and then travels on the downhill, the engine is stopped because of a low required driving force, the vehicle travels almost without using the power of the motor, and the driving battery is charged through regenerative operation of the motor generator. In this period (t2 in the drawing), information for calculating an electric power consumption rate (an electric power consumption and a travel distance) is acquired as the engine is stopped, so an electric power consumption per unit travel distance in this period is relatively small, and the electric power consumption rate is calculated to be relatively good. In this period t2, as indicated by the alternate long and short dash line in the drawing, the electric power consumption rate gets better as the vehicle travels; however, the electric power consumption rate contains an error (D1 in the drawing) of the electric power consumption rate at the time when the vehicle is travelling on the uphill, so a finally obtained electric power consumption rate includes a deviation D1 toward a side at which the electric power consumption rate gets better with respect to an intrinsically calculated value, and it may be not possible to accurately obtain a distance-to-empty (a distance that can be traveled for a current state of charge of the driving battery) (it may cause an error to extend the distance-to-empty). The error is due to the fact that the potential energy of the vehicle of which the level is raised by the power of the engine at the time of travelling on the uphill is used at the time of travelling on the downhill.
On the other hand, when the plug-in hybrid vehicle HV uses only the power of the motor at the time of travelling on the uphill, the engine is stopped in the period t1, so information for calculating an electric power consumption rate (information about an electric power consumption and a travel distance) is acquired. Therefore, the electric power consumption rate in this period t1 is accurately calculated (coincides with the solid line in the drawing). On the other hand, after the vehicle travels on the uphill, when the engine is driven at the time when the vehicle travels on the downhill, information for calculating an electric power consumption rate (information about an electric power consumption and a travel distance) is not acquired in the period t2. That is, the electric power consumption rate in this period t2 is constant (remains unchanged) as indicated by the alternate long and two short dashes line in the drawing. However, in this period t2, actually, the vehicle travels on the downhill and, therefore, the electric power consumption per unit travel distance is relatively small. If an electric power consumption rate is calculated by acquiring information about an electric power consumption and a travel distance, the electric power consumption rate becomes relatively good (intrinsically, in the period t2, a variation in electric power consumption rate becomes the one indicated by the solid line). Therefore, a finally obtained electric power consumption rate includes a deviation D2 toward a side at which the electric power consumption rate gets worse with respect to an intrinsically calculated value, and, in this case as well, it may be not possible to accurately obtain a distance-to-empty (a distance that can be traveled for a current state of charge of the driving battery) (it may cause an error to reduce the distance-to-empty). Note that a situation in which the engine is driven at the time when the vehicle HV travels on a downhill may be, for example, a situation that, when input limit of the driving battery is reached (Win limitation) as a result of charging of the driving battery through regenerative operation of the motor generator, the engine is subjected to motoring (the engine is rotated by the electric motor) and electric power is consumed by the electric motor (discharged from the battery).